1. Field of the Invention
The present invention relates to anti-fuse circuitry, and in particular to programmable voltage controlled anti-fuse circuitry.
2. Background of the Invention
Fuses and anti-fuses are used in multiple applications to allow internal connections on an integrated circuit to be modified after the process flow has been completed. Such fuses may be programmed by a programming signal to change the state of the connection between two points. Whereas a fuse is a switch which is normally closed, and can be opened by programming such that no current flows through the fuse, an anti-fuse is a switch which is normally open, and can be closed by programming, such that the voltage across the anti-fuse becomes close to zero.
There are a number of different known types of fuses and anti-fuses. For example, a poly-silicon fuse comprises a region of poly-silicon that can be destroyed by an electrical signal. A drawback of this type of fuse is that it is unreliable, meaning that it may not keep its programmed state throughout its lifetime. A gate oxide anti-fuse is an anti-fuse essentially formed as a capacitor, having a dielectric which is broken by increasing a voltage across the electrodes of the capacitor. A drawback of this solution is that a high voltage is required to break-down the dielectric, higher than the normal voltages used on the integrated circuit, and thus requires specific technology adapted to function at the higher voltages. In many semiconductor technologies, such specific technology is not easily available. A laser fuse comprises a metal rod that can be destroyed by a laser. A drawback of such a fuse is that it cannot be programmed outside the process flow, in other words in the final application.
A further drawback of the above solutions is the chip area they consume, and their power consumption which is relatively high.
There is thus a need for a reliable solution without the drawbacks of these known solutions.